Activation of Beta-adrenergic Receptors\u27 Role in Formation of Enhanced Contextual Memory

The role of beta-adrenergic receptor (β-AR) activation following emotionally arousing events has previously been demonstrated to play a role in the formation of enhanced memory. The mechanism by which β-AR activation leads to enhanced fear memory is still unknown; however, one possible mechanism is the induction of interleukin-1 (IL-1) at a low concentration. Activation of β-ARs causes a release of IL-1 within the basolateral amygdala (BLA), which is predicted to play a key role in the pathway of enhanced memory formation following an emotionally arousing event. To test this hypothesis, we attempted to replicate previous findings that the beta-adrenergic agonist, isoproterenol, administered following exposure to contextual fear conditioning would enhance the formation of the fear memory. Following training in a fear conditioning paradigm, twelve rats (6 females, 6 males) were either given 5.0mg/kg isoproterenol (β-AR agonist) or vehicle via intraperitoneal (IP) injection and returned to their cages. After 24 hours, each rat was resubmitted to the operant box for fifteen minutes and freezing behavior measured to test for the formation of enhanced fear memory. A significant increase in freezing was observed in male rats compared to females; however, contrary to expected results, no difference was found between isoproterenol-treated animals compared to controls. Additional studies are verifying that isoproteneral actually increased brain IL-1.